原状粉煤灰对超高性能混凝土性能的影响

为提高粉煤灰的综合利用率,降低原料成本,采用未经磨细和分选的原状粉煤灰等质量替代硅灰来制备超高性能混凝土(UHPC),并研究了不同掺量的原状粉煤灰对UHPC力学性能及微观结构的影响。结果表明:原状粉煤灰的掺入可使UHPC中胶凝材料的粒度呈梯度分布,形成良好的微级配;并且使新拌混凝土的流动度增大,影响了钢纤维在UHPC基体中的分布;当原状粉煤灰掺重不超过30%时,UHPC抗折强度随着原状粉煤灰掺量的增加呈现不同程度的增长,30%原状粉煤灰掺量的UHPC抗折强度与不掺粉煤灰的空白样相比提高了34%;由于原状粉煤灰水化缓慢,当原状粉煤灰掺量在0%~40%时,UHPC抗压强度随着原状粉煤灰掺量的增加有所下降。孔结构分析表明:UHPC的平均孔径以及总孔体积均随着原状粉煤灰的掺入而减小,基体更加密实;当原状粉煤灰掺量为30%时,SEM照片显示钢纤维与UHPC基体结合紧密,界面黏结增强。

Effect of Raw Fly Ash on Performance of Ultra-High Performance Concrete

In order to improve the comprehensive utilization rate of fly ash and reduce the cost of raw materials,ultra-high performance concrete(UHPC)was prepared by the mass fraction of raw fly ash without grinding and sorting instead of silica fume.The effects of different amounts of raw fly ash on the mechanical properties and microstructure of UHPC were studied.The results show that the particle size distribution of cementitious material in UHPC is gradient,and good micro-grading can be formed by the addition of raw fly ash.The fluidity of fresh concrete increases and the distribution of steel fiber in UHPC matrix is affected.When the raw fly ash content does not exceed 30%,the flexural strength of UHPC increases in varying degrees with the increase of raw fly ash content.Compared with the blank sample without fly ash,the flexural strength of UHPC with 30%raw fly ash increases by 34%.In the range of 10%to 40%content of raw fly ash,due to the slow hydration of raw fly ash,the UHPC compressive strength decreases with the increase of replacement content of raw fly ash.The pore structure analysis shows that the average pore size and total pore volume of UHPC decrease with the addition of raw fly ash,and the matrix is more dense.When the raw fly ash content is 30%,SEM images show that the steel fiber is closely combined with UHPC matrix and the interfacial adhesion is enhanced.